1. Field of the Invention
The present invention relates to a golf club shaft.
2. Description of the Related Art
A so-called carbon shaft has been known as a golf club shaft. A sheet winding method has been known as a method for manufacturing the carbon shaft. In the sheet winding method, a laminated constitution is obtained by winding a prepreg (prepreg sheet) around a mandrel.
In the shaft, material error and error of a winding operation or the like may cause variation. In particular, the errors may cause circumferential variation. In particular, the error may cause variation in a flex (flexural rigidity) in a circumferential direction. When the variation exists, the flex is changed by a circumferential relative position (hereinafter, also referred to as a shaft position) of a shaft to a head. The variation may cause various problems.
A technique for improving circumferential uniformity is disclosed. Japanese Patent Application Publication No. 2705047 (U.S. Pat. No. 5,427,373) discloses a shaft having sheets having both end parts made abut on each other without overlapping both the end parts. The abutted portions are substantially equally dispersed in a circumferential direction. Japanese Patent No. 3315338 discloses a tubular body in which an overlapping part of adjacent layers is located on an opening part. The invention described in Japanese Patent No. 4510260 specifies that a winding end edge of a prepreg (P2) is made to abut on a winding start edge of a prepreg (P1).
Japanese Patent Application Laid-Open No. 2009-254401 discloses a shaft having a first angle layer and a second angle layer. The orientation angle of a fiber in the second angle layer is 60 degrees to 75 degrees with respect to the longitudinal direction of the shaft. It is an object of Japanese Patent Application Laid-Open No. 2009-254401 to improve torsional strength while maintaining the characteristic and the outer diameter of a conventional shaft.
On the other hand, a golf club having a head and a shaft attachable to and detachable from each other has been developed.
In the typical example of this type of golf club, a sleeve is bonded to a tip part of a shaft. The sleeve is engaged with a rotation preventing part of a head, and is locked by a screw. The shaft can be inclined to the sleeve in the golf club. The inclination enables adjustment of a loft angle, a lie angle, and a face angle. That is, the loft angle, the lie angle, and the face angle can be adjusted by changing a shaft position.
In this type of golf club, particularly, the variation of the shaft causes a problem. That is, it is not preferable that the flex is changed depending on the shaft position.